1. Field of the Invention
The present invention relates to an LED lighting apparatus with improved harmonic distortion components of a source current, and more particularly, to an LED lighting apparatus, which increases a power factor by improving a total harmonic distortion (THD) of an input current in such a manner that a waveform of the input current output from a rectification block is made maximally close to a sine wave by using a path selection switch and a charging/discharging block, and improves the lifespan and luminous intensity uniformity of LED elements by actively changing a series/parallel connection relationship among a plurality of LED groups according to a voltage level of a rectified voltage.
2. Description of the Related Art
A light emitting diode (LED) is a semiconductor element that is made of a material such as Ga, P, As, In, N, and Al. The LED has a diode characteristic and emits red light, green light, or yellow light when a current flows therethrough. Compared with a bulb or lamp, the LED has a long lifespan, a fast response speed (time until light is emitted after a current flows), and low power consumption. Due to these advantages, the LED has tended to be widely used.
In general, a light emitting element could be driven only at a DC voltage due to the diode characteristic. Therefore, a light emitting device using the light emitting element is restrictive in use and must include a separate circuit, such as SMPS, so as to use an AC voltage that has been used at home. Consequently, the circuit of the light emitting device becomes complicated and the manufacturing cost of the light emitting device increases.
In order to solve these problems, much research has been conducted on a light emitting element that can also be driven at an AC voltage by connecting a plurality of light emitting cells in series or in parallel.
FIG. 1A is a block diagram illustrating a configuration of a conventional LED lighting apparatus, and FIG. 1B is a waveform diagram illustrating waveforms of a rectified voltage and a rectified current in the conventional LED lighting apparatus of FIG. 1A.
As illustrated in FIG. 1A, the conventional LED lighting apparatus includes an AC power source VAC, a rectification block 10, and an LED block (LED array) 20. The rectification block 10 receives an AC voltage from the AC power source VAC and performs a full-wave rectification to output a rectified voltage Vrec. The LED block 20 includes one or more LEDs that receive the rectified voltage Vrec from the rectification block 10 and emit light. In general, even when the rectified voltage Vrec is applied from the rectification block 10, no current flows from the rectification block 10 to the LED block 20 due to the component characteristic of the LED until before a threshold voltage level VTH capable of driving the LED block 20 is applied. Consequently, in a period during which the voltage level of the rectified voltage Vrec is lower than the threshold voltage level VTH, a current Irec does not flow through the LED block 20. Hence, as illustrated in FIG. 1B, the current Irec output from the rectification block 10 does not have a sine waveform, and a total harmonic distortion (THD) characteristic is bad. In addition, in the case of the conventional LED lighting apparatus, the LED block 20 emits light only in a period during which the voltage level of the rectified voltage Vrec is equal to or higher than the threshold voltage level VTH. Therefore, a power factor is deteriorated. In order to solve these problems, a power factor correction (PFC) circuit may be added to the LED lighting apparatus of FIG. 1A. However, in this case, the size of the LED lighting apparatus increases, and the manufacturing cost of the LED lighting apparatus rises. Also, the circuit configuration of the LED lighting apparatus becomes complicated.
Furthermore, although not illustrated, the conventional LED lighting apparatus may include a plurality of LED arrays and may be configured to perform a so-called sequential driving scheme that sequentially turns on/off the plurality of LED arrays according to the voltage level of the rectified voltage. However, in the case of the LED lighting apparatus using the conventional sequential driving scheme, since the light emission periods of the plurality of LED arrays are different, the luminous intensity uniformity of the LED lighting apparatus is degraded and the lifespan of the LED arrays becomes disproportionate. Therefore, the lifespan of the LED lighting apparatus is subjected to the LED array having a relatively long emission time.